A liquid discharge head applied for the ink jet recording system (liquid discharge recording system) for recording by discharging a recording liquid such as an ink in general comprises a liquid flow path, a liquid discharge energy generating part provided in a part of the liquid flow path, and a minute recording liquid discharge port for discharging the liquid in the above-mentioned liquid flow path by the thermal energy of the liquid discharge energy generating part (hereinafter it is referred to as the “orifice”).
Conventionally, as a method for manufacturing such a liquid discharge recording head, for example, Japanese Patent Application Publication No. H06-45242 discloses a method for manufacturing an ink jet head, comprising the steps of patterning a mold of an ink liquid flow path with a photosensitive material on a substrate with a liquid discharge energy generating element formed, then applying and forming a coating resin layer on the above-mentioned substrate so as to coat the mold pattern, forming an ink discharge port communicating with the mold of the above-mentioned ink liquid flow path on the coating resin layer, and thereafter removing the photosensitive material used for the mold (hereinafter, it is also abbreviated as the “mold injection method”). According to the production method for a head, a positive type resist is used as the photosensitive material from the viewpoint of the removal easiness. Moreover, according to the production method, since the semiconductor photolithography technique is adopted, an extremely highly accurate and minute process is enabled for the formation of the ink liquid flow path, the discharge port, or the like. However, according to the production method adopting the semiconductor production method, basically, the shape change in the vicinity of the ink liquid flow path and the discharge port is limited to the change in the two-dimensional direction parallel to the element substrate. That is, since the photosensitive material layer cannot be provided partially in a multiple layers due to the use of the photosensitive material for the mold of the ink liquid flow path and the discharge port, a desired pattern with the change in the height direction cannot be obtained in the mold for the ink liquid flow path, or the like (the height direction shape from the element substrate is uniformly limited). As a result, it becomes the limitation in the ink liquid flow path design for realizing the high speed and stable discharge.
As a technique for solving the same, Japanese Patent Application Laid-Open No. 2003-25595 proposes forming an intermediate chamber with dissolvable resins in two layers and the cross-sectional area in the discharge port lower part that is enlarged (an intermediate portion narrower than the substrate side liquid flow path and wider than the discharge port top end part is provided between the substrate side liquid flow path and the discharge port top end). Moreover, the official gazette discloses a specific example of using a thermally cross-linkable positive type resist including a PMMA (polymethyl methacrylate) for the lower layer of the removable two layer resins and using a PMIPK (polymethyl isopropyl ketone) for the upper layer.
On the other hand, Japanese Patent Application Laid-Open No. 2004-042396 discloses a method for manufacturing an ink jet recording head using for the liquid flow path forming mold material, a copolymer of an ester methacrylate and a methacrylic acid as a thermal cross linking factor as the resin used for a solid layer for manufacturing a mold for forming the liquid flow path. Furthermore, Japanese Patent Application Laid-Open No. 2004-42650 discloses a method for manufacturing an ink jet recording head using for the mold material for forming a liquid flow path, a thermally cross linkable positive type resist as a copolymer of a methacrylic anhydride as a factor for widening the sensitive area, including an ester methacrylate.
By forming the mold material for forming a liquid flow path of a liquid discharge head in a two layer laminated structure using two kinds of positive type resists, the flexibility in designing the minute liquid flow path structure for a liquid discharge head can be widened. However, for providing a further minute liquid discharge head structure, a technique for forming a minute structure further accurately is called for. For example, in some cases the lower layer of the mold material for the liquid flow path comprising the two-layer structure may need to be thick to some extent. In this case, if the positive type resist for forming the lower layer of the mold material for the two layer structure liquid flow path is thermally cross linkable type as disclosed in Japanese Patent Application Laid-Open Nos. 2003-25595, 2004-042396 and 2004-42650, there would be many limitations in terms of the design and the production method, such as:    1. the difficulty in providing a thick film due to the film stress limitation (maximum: 10 μm is the limit);    2. generation of cracking at the time of forming a pattern (cracking in the bent pattern derived from the stress alleviation at the time of the development);    3. generation of cracking, or the like due to application shock derived from the grade difference on the substrate by applying a coating solution including a solvent onto a thermally cross linkable film;    4. increase of the necessary exposure amount at the time of patterning due to reduction of the decomposition rate by the exposure by the mesh like three-dimensional structure at the time of the thermally cross linkable film formation; and    5. increase of the exposure amount for decomposition at the time of finally removing the mold material.